1. Field of the Disclosure
The present disclosure relates generally to a technique for interference cancellation for a User Equipment (UE) in a wireless communication system, and more particularly, to a technique for canceling interference based on interference parameter blind detection of a subframe in which a traffic signal is transmitted in a Network-Assisted Interference Cancellation and Suppression (NAICS) scheme.
2. Description of the Related Art
To satisfy the strict requirements of the International Telecommunication Union Radio communication Sector (ITU-R), next-generation wireless networks such as, for example, Long Term Evolution (LTE)-Advanced (LTE-A), have been designed to support a broad bandwidth having a maximum of 100 MHz with higher-order spatial multiplexing and Carrier Aggregation (CA) up to 8 layer and 4 layer, respectively, in a DownLink (DL) and an UpLink (UL).
However, spatial frequency reuse using more cells provides a larger capacity gain than a cell having an increased spatial order or spectrum bandwidth. Thus, heterogeneous networks using small cells in a macro cell environment have emerged as the most practicable development path for next-generation wireless networks.
Although these heterogeneous networks may provide various advantages, they may cause unprecedented challenges to wireless networks. In particular, interference management, which is a matter of the utmost concern, may increase significantly. In this context, advanced co-channel interference aware signal detection has been researched in a recent development process for LTE-A systems. When cells are very densely disposed in heterogeneous networks, inter-cell interference becomes more serious, causing significant problems to the wireless networks.
Various attempts have been made to solve such problems.
An enhanced Inter-Cell Interference Coordination (eICIC) technique has been proposed to alleviate interference between macro cells for a UE that is located closer to small cells.
In addition, a concept of an Almost Blank Subframe (ABS) has been introduced as a Base Station (BS)-based interference alleviation method. When a BS indicates that a subframe is an ABS, a macro cell does not perform transmission in pilot signals. Specifically, a macro cell does not perform transmission in a DL data channel, that is, a Physical Downlink Shared Channel (PDSCH), except for a Cell-Specific Reference Signal (CRS), thus alleviating interference.
In addition, for a UE, a UE-based interference alleviation scheme using CRS sequence awareness is under consideration. A Further Enhanced Inter-Cell Interference Coordination (FeICIC) technique, which permits CRS Interference Cancellation (CRS-IC) by the UE, has been established in the LTE Release 11 of the 3rd-Generation Partnership Project (3GPP).
An NAICS technique has been studied by the 3GPP. Inclusion of a work item referred to as “NAICS” in the LTE Release 12 is under consideration. It has become obvious from studies that significant performance gain can be achieved on the assumption that interference parameters are known to a UE by broadcasting or dedicated signaling (for example, upper-layer signaling such as Radio Resource Control (RRC)) or the newly defined Downlink Control Information (DCI). However, the success of NAICS based on signaling depends on making interfering BSs use signaled parameters such as Rank Indicator (RI), Precoding Matrix Indicator (PMI), and Modulation Level (MOD), potentially limiting scheduling flexibility for neighboring cells. A back-haul capacity between BSs and a control channel capacity from the BS to the UE are generally limited, and support for an interference parameter is not maintained in actual systems at all times.
To overcome disadvantages such as a scheduling restriction of a cell and a network signaling overhead, the UE may estimate interference parameters from received signals as blind parameters. Joint Blind Detection (BD) of RI, PMI, and MOD may apply a Maximum Likelihood (ML) estimation including an exhaustive search among all possible combinations of RI, PMI, and MOD designated in the LTE systems. In LTE-Orthogonal Frequency Division Multiple Access (LTE-OFDMA) systems, assigned RI, PMI, and MOD may differ across simultaneously scheduled UEs from Transmission Time Interval (TTI) to TTI in a time domain and from Resource Block (RB) to RB in a frequency domain. Thus, joint BD would be required to be performed for every RB in every TTI in the LTE DL systems.
However, this assumption means that the interference parameters may dynamically change from one RB to another RB in the frequency domain in very TTI according to channel conditions, limiting scheduling performance and excessively increasing a network signaling load.